Malnutrition in experimental animals clearly affects a specific, functionally-important class of brain compounds, the neurotransmitters. This has been shown to be the case when the dietary content of a high-quality protein (e.g., casein) is reduced; it also occurs when the dietary protein is of poor nutritional quality. Our studies focus on a protein of low nutritional quality, corn, which is extremely deficient in tryptophan. The chronic ingestion by post-weanling rats of a diet containing corn as the sole protein source leads to substantial reductions in the brain concentrations of serotonin, a neurotransmitter derived from tryptophan. This effect appears to result from a diet-induced deficiency in-brain tryptophan, and has already been shown to cause a particular change in a brain function related to serotonin neurons; i.e., an increase in pain sensitivity. We now hope to explore this line of investigation further, to study the biochemical deficits in the brain that contribute to the reduction in brain serotonin, to determine whether another set of important brain outputs, the secretions of certain pituitary hormones (growth hormone, prolactin, vasopressin), which are controlled in part by serotonin neurons in the brain, are modified by corn malnutrition, to assess whether the chronic ingestion of other normal dietary proteins, such as gluten and soyprotein, which have unusual amino acid compositions, produce predictable changes in brain amino acids and neurotransmitters, and to explore the possibility that corn malnutrition, begun during prenatal life, reduces brain serotonin prenatally and/or postnatally. These studies should contribute to our understanding of the mechanisms by which altered protein nutrition modifies brain function, and, hopefully, aid in the development of therapies for human populations suffering from similar forms of malnutrition.